Ferrous alloys containing bismuth



Patented June 19, 1945 UNITED STATES txamm PATENT OFFICE FEKROUS ALLOYS CONTAINING BISMUTH Pennsylvania No Drawing. Application January 11, 1944, Serial No. 517,842

- imum recovery. However, larger particles may 4 Claims.

This invention relates to steels and particularly to steels which are to be subjected to machining operations.

The essence of the invention lies in the discovery that the addition of bismuth to steels of various compositions has a beneficial effect upon their machining characteristics, as will be more fully pointed out hereinafter.

It is therefore an object of this invention to provide a steel which has improved machining characteristics in comparison with ordinary steels.

A further object of this invention is to provide ferrous materials containing effective amounts of bismuth and exhibiting superior machinability characteristics to similar alloys not containing bismuth.

Other objects of this invention will appear from the following detailed description thereof.

For the purposes hereof, a tool force test and a cutting speed test have been arbitrarily selected in order to compare the machinability of steels embodying the present invention with those of the prior art. In the tool force test, samples were machined at a constant speed and rate of feed, using a tool of standard shape mounted at one end of a pivoted arm, the other end of the arm being connected to a hydraulic gauge by which the force upon the tool was measured. In the tool life test, the samples under test were machined with a tool of standard shape and at a standard depth of cut and rate of feed until tool failure occurred. This test was carried out at various speeds and the results plotted graphically, from which graph the rate of speed for an arbitrarily chosen tool life could be determined. In the following tables the symbol v is used to indicate the machining speed, in surface feet per minute, which will result in tool failure after ten minutes of operation.

As heretofore stated, this invention is based on the discovery that the addition of bismuth to steel has a pronounced beneficial efiect on its machining characteristics. The amount of bismuth necessary to produce such benefit is very small, as little as .045% being markedly efiective.

The bismuth may be added to the steel in the furnace, or in the ladle, or while pouring the steel into the mold. Preferably the bismuth is added while the steel is being poured into the mold since this method of addition seems to result in a larger recovery of the bismuth and to reduce the amount of segregation. It has been found that the addition of metallic bismuth in finely divided form (20-30 mesh) gives the maxbe used. 111% bismuth may be added as a pure metal or in e form of enemies. compounds of bismuth (sulfide, etc.) or alloyed with other metals, such as a bismuth-lead alloy or a bismum-manganese alloy.

Table I illustrates some of the advantages of the invention. In the heats reported in Table I, bismuth was added in varying amounts to steel containing about .12% carbon. In heats 3 and 4 the bismuth was added in the form of a bismuth-lead alloy and in heats 5 and 6 the bismuth was added in the form of a bismuth.- manganese alloy. The results of tool force tests on the resulting alloys are shown in Table I, and indicate the decreased tool force characteristics of the steels containing bismuth in comparison with the bismuth-free steel.

Table I Heat No 0 Mn s Bl Pb ,'g},ffg

In addition to decreasing the tool force, the addition of bismuth increases the permissible machining speed for a given tool life. Table 11 illustrates the efiect of bismuth addition to a number of heats of steel, containing sulphur in amounts usual in so-called free cutting steels.

The results shown in Table II are:

Table II Vw (surface Heat No. 0 Mn Si 5 Bi feet per minute) 1 Estimated. 1 Estimated from amount of blsmuth added to heat.

By way of further example, it has been found that SAE X-lll2 steel containing .10% carbon,

.83% manganese, .089% phosphorus and 32% sulphur shows 9. vii) value of 266 surface feet per minute, while a steel of the same composition, but containing .18% bismuth, shows a V10 value of 323 surface feet per minute.

From the foregoing, it is apparent that the addition of small quantities of bismuth to ferrous materials has a marked beneficial effect on the machinability ofsuch materials.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A steel containing carbon in effective amounts up to 1.7%, from .10% to .50% sulphur, and from .01% to 1.0% bismuth.

2. A steel containing carbon in effective amounts up to 1.7%, from .10% to .50% sulphur, from .01% to 2.0% manganese and from .01% to 1.0% bismuth.

3. A steel containing between .05% and 25% carbon, between .30% and .75% manganese, between .05% and .15% silicon, between .10% and .50% sulphur and between .01% and 20% bismuth.

4. A steel containing carbon in effective amounts up to 1.7%, between .01% and 2.0% manganese, between .06% and .50% sulphur and between .01% and .50% bismuth.

JAMES L. GREGG. ERIC R. M. 

